1. Field of the Invention
This invention relates to two-cycle engines in which a hollow wrist pin received in a piston and connecting a connecting rod to the piston is so arranged that during the movement of the piston, an axis of the wrist pin is movable into a plane passing exhaust and scavenge ports.
2. Prior Art
Utility Model Publication No. 50-20193 discloses one example of conventional two-cycle engines in which axes of exhaust and scavenge ports in a wall of a cylinder are disposed transversely of a hollow wrist pin which connects one end of a connecting rod to a piston movable along the cylinder. From the viewpoint of design, there are occasions when exhaust and scavenge ports need to be positioned in opposed relation to each other in such a manner that opposite ends of the hollow wrist pin, received in a transverse hole through the piston, is brought into registry with the opposed exhaust and scavenge ports during the movement of the piston along the cylinder. Therefore, the opposed exhaust and scavenge ports are brought into communication with each other via an axial bore of the hollow wrist pin during the operation of the engine. As a result, a fuel-air mixture in a crankcase is caused to be fed directly to the exhaust port through the scavenge port and the hollow wrist pin on the downward stroke of the piston to by-pass the combustion chamber. In addition, since the exhaust port is brought into communication with the interior of the crankcase, the exhaust gas is caused to flow thereinto, so that a residual pressure wave of the exhaust gas in an exhaust pipe is attenuated. The residual pressure wave or reflected pressure wave serves to force a blowby gas, tending to flow from the combustion chamber, back thereinto to achieve a good charging efficiency. Further, the flowing of the exhaust gas into the crankcase will dilute the fuel-air mixture.